1. Field of the Invention
This invention relates to a process for producing trialkanolamines by the reaction of an alkylene oxide with liquefied ammonia in the presence of a zeolite catalyst. More particularly, this invention relates to a process for producing a high purity trialkanolamine excellent in hue by two-stage vacuum distillation of a crude trialkanolamine.
Further, this invention relates to a process for refining a trialkanolamine from a mixed alkanolamine obtained by the reaction of an alkylene oxide with ammonia. More particularly, this invention relates to a process for adding a low-boiling compound to a raw material trialkanolamine and subsequently distilling them together.
2. Description of Related Art
As a commercial way of producing ethanolamine by the reaction of ethylene oxide with ammonia, a process of the reaction of ethylene oxide with aqueous ammonia (aqueous ammonia process) has been in high vogue. This process forms three kinds of product, monoethanolamine, diethanolamine, and triethanolamine. To acquire triethanolamine, therefore, the monoethanolamine, diethanolamine, unreacted ammonia, and water contained, must be separated by vacuum distillation. The crude triethanolamine thus obtained is vacuum distilled because it contains 4–8% of diethanolamine and 0.1–1% of a high-boiling substance. In the distillate recovered, the initial fraction contains diethanolamine and the final or post fraction contains the high-boiling compound both in high concentrations, so that this vacuum distillation produces high purity triethanolamine only in a low yield.
Since the market trend of ethanolamine has changed in recent years, the production balance between diethanolamine and triethanolamine manufactured from the aqueous ammonia process can no longer correspond with the change. To be specific, the demand for diethanolamine, which is used as the raw material for herbicide, is going up greatly, whereas the demand for triethanolamine is reducing on account of the problem of toxicity. To adjust the balance between these demands, a new process other than the aqueous ammonia process for the production of ethanolamine has been developed.
In the production of ethanolamine, a product which is composed of mon-/di-/triethanolamine at a weight ratio of 55/41/4 is obtained by causing ammonia and ethylene oxide to react at a molar ratio of 7:9 while using pentacyl type aluminosilicate (crystal structure MFI type) as a zeolite catalyst (U.S. Pat. No. 6,169,207) (catalyst process).
As a way of reducing coloration in triethanolamine, a process has been proposed which includes heat-treating triethanolamine in the absence of oxygen but in the presence of an inorganic compound such as silicon and aluminum, and subsequently distilling the resultant product (JP-B-05-8693).